High performance wheel rims for bicycles in particular, mountain bike, are generally formed by an extrusion process to provide a continuous length of extruded material that is coiled which then cut into rim forming members, i.e. discrete lengths each of which is formed into a hoop or circular rim with its ends joined together to form an annular wheel rim. One such technique for manufacturing rims is described in European patent application 0429104 A1 published May 21, 1991, inventor Best et al.
Friction or force fit pin joints are one of the more popular type of joints used to connect the ends of an extruded rim member together to form the circular wheel rim. Normally, such pin joints demand the use of thick walled passages into which the pins are forced. The requirement for thick walled passages is to limit deformation of the rim, since any distortion of the rim in a high performance bicycle, acts negatively on performance and may result in poor brake performance such as brake grabbing.
Recently issued U.S. Pat. No. 5,470,133 issued Nov. 28, 1995 to Kuo et al. shows what is described as an improved force pin joint wherein a specific type of threaded pin is used, in this case, rotating pins which tend to wind themselves into the holes or passages on opposite sides of the joint as the ends of the rim member are forced together to form the wheel rims. These pins are stated to produce a better joint than is obtainable using simple force fit pins.
The concept of using force fit pins joints similar to that described in the U.S. Pat. No. 5,470,133 (but without threads) is shown in the U.S. Pat. No. 4,938,540 issued Jul. 3, 1990 to Sacks. This patent describes a solution to a further problem that is sometime encountered, namely, leakage of fluids into or out of the passages formed in the rim member and into which the pins are received. In this patent, an epoxy resin or the like is used to form a hermetic seal sealing the opposite ends of the passage, i.e. around the joining pin) so there can be no leakage into or for that matter, out of the passage.
Rim weight is a very important consideration in high performance bicycle, such as high performance mountain bikes, thus, the lighter the rim, provided it meets the other structural requirements, the better. Clearly, to produce a lighter rim from a given material requires the amount of material used in the rim be reduced to a minimum. However, as above indicated, when the wall thickness is too small and force fit pins are used such as force fit pins described by Sacks or Kuo et al., the rim becomes deformed by the pins thereby leaving a high spot or expanded area on the lateral surface of the wheel rim which particularly if not properly dealt with in the finishing operation may interfere with the smooth operation of the brakes.